Conventionally, a film formed from a composition comprising an ethylene-unsaturated ester copolymer (hereinafter abbreviated to an ethylene-unsaturated ester copolymer film) such as an ethylene-vinyl acetate copolymer (hereinafter abbreviated to EVA) is used for forming a laminate in the form of a solar cell sealing film and an intermediate film for a laminated glass. When an ethylene-unsaturated ester copolymer film is used in an intermediate film for a laminated glass by interposing between glass plates, the film shows functions such as penetration resistance (passing through resistance) and prevention of scattering of broken glass. Further, when the film is used in a solar cell sealing film by arranging on the front side and the backside of photovoltaic elements, the film shows functions such as ensuring an electrical insulation property and a mechanical durability.
A laminated glass is, for instance, as shown in FIG. 3, prepared by interposing an intermediate film 5 between glass plates 7A and 7B to give a laminate, and preliminary pressing the laminate under reduced pressure to degas remaining air in each layer, and subsequently pressing it under heating whereby the laminate is adhesively combined.
Furthermore, a solar cell is generally, as shown in FIG. 4, prepared by superposing a transparent front side protection material 11 (e.g., glass plate), a front side sealing film 13A, plural photovoltaic elements 14 (e.g., photovoltaic elements made of silicon), a backside sealing film 13B and a backside protection material 12 (backside covering member) in this order to give a laminate, and preliminary pressing the laminate under reduced pressure to degas remaining air in each layer, and subsequently pressing it under heating whereby the laminate is adhesively combined by crosslinking or curing a front side sealing film 13A and a backside sealing film 13B.
The ethylene-unsaturated ester copolymer films need to be free from occurrence of the phenomenon that the films adhere to each other to form a block during storage of the films (hereinafter referred to as blocking). Furthermore, the films need to have a good workability in the laminating step in the process for preparing the laminates such as a laminated glass and a solar cell, and a good degassing property in the preliminary pressing step. In case the degassing is insufficient, reduced transparency of the resultant laminated glass, and reduced generating efficiency of the resultant solar cell may occur. Furthermore, the resultant solar cell is apt to be insufficient in durability, and to blister in long-term use.
An intermediate film for a laminated glass and a solar cell sealing film having a fine concavo-convex shape pattern (referred to as emboss) on one surface or both surfaces of the film have been developed (Patent Documents 1 and 2). The films correspond to an ethylene-unsaturated ester copolymer film satisfying the above-mentioned requirements. Furthermore, for example, as a process for preparing a film provided with emboss on both surfaces of the film, a process for preparing a film, wherein relationships among a surface roughness of one roll surface and another roll surface of a pair of emboss rolls (i.e., rolls for providing emboss to the film), a roll temperature and a pressure exerted by rolls are defined, has been developed (Patent Document 3).